1. Field of the Invention
The invention is directed to an improved fuel injection system for an internal combustion engine.
2. Description of the Art
One fuel injection system, known from German Patent Disclosure DE 198 53 103, has a high-pressure pump, by which fuel is pumped at high pressure into a reservoir. Injectors disposed on engine cylinders communicate with the reservoir. A feed pump is provided, by which fuel is pumped out of a fuel tank to the intake side of the high-pressure pump. A fuel metering device triggered by an electronic control unit is provided, which is disposed in the communication between the compression side of the feed pump and intake side of the high-pressure pump. The fuel metering device serves to control the fuel quantity pumped into the reservoir by the high-pressure pump, as a function of engine operating parameters. The fuel metering device has a regulating valve, which has a slidelike valve member that is movable by an electromagnet counter to a restoring spring. In cooperation with an outflow opening of the valve housing, the valve member, via its outer jacket and as a function of the stroke, controls a flow cross section in the communication between the feed pump and the high-pressure pump. Throttling of the fuel flow that is flowing to the high-pressure pump is the result. The pressure generated by the feed pump drops in the process, so that the high-pressure pump comes to be filled only partly. The high-pressure pump has poor efficiency as a result. Under certain engine operating conditions, such as in overrunning, the high-pressure pump must not pump any fuel into the reservoir, and this state is known as zero pumping. However, it cannot be assured that the inlet for fuel from the feed pump to the high-pressure pump will be completely closed by the regulating valve, and thus additional provisions are necessary to carry away fuel, pumped by the feed pump and passing through the regulating valve, so that the fuel will not be pumped into the reservoir by the high-pressure pump and so that the zero pumping state will be achieved. These additional provisions in turn worsen the efficiency of the fuel injection system, since some of the fuel pumped by the feed pump flows constantly out in the form of a leakage flow.